Wave motions in the sea and large lakes are a potential energy source which till now is very little utilized. The available wave energy depends on the wave height and is naturally different for different locations. The average wave energy during a year is dependent on the different wind conditions, which are highly influenced by the distance of the location from the nearest coast. Measurements have, among other things, been made in the North Sea. At a measuring point approx. 100 km to the west of the coast of Jutland where the depth was approx. 50 m, measurings of the wave height have been made.
In order to utilize the energy that is available by the motions of the sea waves, different types of wave power assemblies for the generation of electric power have been proposed. However, these have not succeeded to successfully compete with conventional electric power production. Wave power plants realized hitherto have in the main been test plants or used for local energy supply to navigation buoys. In order for commercial electricity production to be feasible, and thereby give access to the large energy reserve available in the motions of the sea waves, it is not only required that the setting out of the assemblies is carried out in suitably located places. It is also necessary that the assembly is reliable, has high efficiency as well as low manufacturing and operating costs.
Among the feasible principles of the conversion of the wave motion energy to electric energy, a linear generator should in that connection to the largest extent meet these requirements.
The vertical motions of the hull caused by the wave motions can thereby directly be transferred to a reciprocating motion of the rotor of the generator. A linear generator may be made very robust and simple and by it being anchored at the bottom, it becomes solidly unaffectable by streams in the water. The only movable part of the generator will be the reciprocating rotor. By the few movable parts thereof and the simple constructive build-up thereof, the assembly becomes very reliable.
By, for instance, U.S. Pat. No. 6,020,653, a wave power assembly is previously known, which is based on the linear generator principle. Hence, the specification describes a generator anchored at the bottom, which generator produces electric energy from the wave motions of the sea surface. A generator coil is connected to a hull so that the coil moves up and down with the wave motions. A magnetic field acts on the coil when it moves so that an electromagnetic force is generated in the same. The magnetic field is such that it provides a uniform field having a single magnetic orientation along the length of stroke of the entire coil. The generator comprises a base plate on the bottom of the sea that carries the magnetic core in which the coil moves.
Furthermore, a wave power assembly provided with a linear electric generator is previously known by U.S. Pat. No. 4,539,485. The rotor thereof consists of a number of permanent magnets and the winding of the generator is arranged in the surrounding stator.
Further, in PCT/SE02/02405, a wave power assembly is disclosed having a linear generator in which the rotor is permanent magnetic and the stator comprises winding forming a plurality of poles distributed in the direction of motion of the rotor. A spring means is arranged in the form of a tension spring and exerts a downwardly directed tensile force on the rotor, i.e. directed against the lifting force of the hull.
When the hull is lifted by a wave, this entails that the rotor in the generator is pulled upwards. One portion of the energy generated on that occasion is converted to electric energy and one portion is accumulated in the tension spring.
When the hull then moves from a crest of a wave to a trough of a wave, the rotor is pulled downwards by the tension spring. Thereby, the energy accumulated in the spring is converted to electric energy.
When a simple mechanical tension spring is used, the conversion to electric energy will be effected non-uniformly, which creates disturbances and causes inferior conditions for the energy conversion.
The object of the present invention is, against this background, to seek to overcome said problem in a wave power assembly of the kind in question so that the conversion to electric energy is optimized.